Improved OFDMA uplink Frequency offset Estimation via Cooperative Relaying: AF or DcF?

Abstract

This paper evaluates the performance improvement in orthogonal frequency-division multiplexing access (OFDMA) uplink frequency offset estimation achieved with cooperative relaying. The transmission of each source node (node S) can be improved by optimizing the diversity gain through exploiting the cooperation of the other nodes (cooperative relays), and the relays can operate in either the amplify-and-forward (AF) or decode-and-compensation-and-forward (DcF) mode. One or more than one geographically closely located mobile nodes comprise a cooperative group (CG), and the nodes of the same CG cooperate with each other. In each transmission, the role of the relay is to "help" the source node transmit its training sequence, or, in other words, the relay creates a parallel route between the source node and the destination terminal to improve the reliability of the transmission of S. In the proposed cooperative scheme, the total power used to transmit each training sequence, including that consumed in node S and the relay, is kept constant. Based on the interference analysis, the signal-to-interference-plus-noise ratio (SINR) in both the relay and the destination terminal are derived. The AF mode's cooperative scheme always outperforms that of the DcF mode in terms of frequency offset estimation accuracy due to the estimation error propagation in the latter.